As an electronic device which executes given processing using map data, an in-vehicle navigation device is known. In the in-vehicle navigation device, map data necessary for realizing various functions such as map display and route calculation is read from a storage medium such as a CD-ROM or a DVD-ROM (hereinbelow, also abbreviated to “CD/DVD”).
The map data in the CD/DVD supplied to the above in-vehicle navigation device becomes old with the passage of time due to opening of a new road, changes of road shape and traffic regulations, new construction/closure of various facilities and the like. For this reason, the contents of the CD/DVD are updated periodically (for example, once every year) and put on sale. As the procedure, first, map data as original data of the map data to be stored on the CD/DVD (hereinbelow, referred to as “map original data”) is newly generated. Then, after the latest map data has been generated, the map original data is edited with the latest map data, then a new version CD/DVD is generated and put on sale. Note that the editing of the map original data and the generation of CD/DVD mean editing the map original data and writing the edited map data on a blank CD/DVD.
In the conventional in-vehicle navigation device, a user must buy a new version CD/DVD to always obtain latest information.
On the other hand, a map data update system (hereinbelow, referred to as a “difference update system”) is proposed. In this system, difference information (i.e., information on additional/deleted/changed data) between old map data in a CD/DVD in an in-vehicle navigation device and new map data is supplied from an external information center by utilizing wireless communications or the like. Then, the map data of the navigation device is updated with the new contents based on the difference information from the center. In a case where this difference update system is put into practical use, the user of in-vehicle navigation device can always obtain road information based on latest information without buying a latest CD/DVD (for example, See Patent Documents 1, 2 and 3).
[Patent Document 1]
JP-A-2001-109372
[Patent Document 2]
JP-A-2001-109373
[Patent Document 3]
JP-A-2001-67458
However, although the concept of the difference update exists, the difference update of map data is not actually put into practical use. Particular problems which occur in practical use of the system have not been sufficiently studied. Accordingly, the present inventors have studied problems which may occur in a case where the difference update of map data is actually put into practice, and focused attention on the following problem. That is a shift of map data in a connection portion between unupdated map data (old map data) and updated map data (new map data). Seemingly, such shift does not occur between the old and new map data, but it is considered that the shift actually occurs due to the following reasons:
(1) In a case where the position of a road, existing in both the old and new map data, has been changed, a shift occurs when the old and new map data are mixed.
(2) In a case where the position of a road has not been changed but data generating standards in the old and new map data are different, a shift may occur when the old and new map data are mixed. For example, in a case where the accuracy of indication of road position has been improved, a position in the old map data, which was shifted from an actual position, corresponds with or closer to the actual position in the new map data. Further, in a case where the manufacturers of the old and new map data are different, data generating standards may be different.
When such shift occurs, in a connection portion of map data, a road is broken in the middle, thus the initially-continuous road becomes discontinuous. Further, in the case (2), a shift occurs in other map constituent elements as well as roads.
Upon display of map data, where these map constituent elements are shifted in a connection portion between the old and new map, the appearance of the map is very poor. Further, this may cause degradation of map matching accuracy. The map matching is specifying a current position on a road by using current position information detected using a GPS, road shape data of map data and the like. When the above-described shift exists, the road shape supposed to be matched around the map connection portion cannot be specified without difficulty. Further, such degradation of the accuracy of map matching and rapid shape change due to such shift may cause execution of inappropriate right/left turn guidance. In this manner, this problem disturbs execution of appropriate navigation function.